What kind of planets have been found, and where?
Officially named PSR B1620-26c, the planet is notable being the oldest known extrasolar planet. It is believed to have been formed about 12.7 billion years ago (probably only about a billion years younger than the universe itself).
PSR B1620-26c orbits a binary pair of stars. One, the pulsar (PSR B1620-26), is a neutron star. The second is a white dwarf with a mass of 0.34 solar mass. These stars orbit each other at a distance of 1 AU about once every half year.PSR B1620-26 is located in the Messier 4 (M4 globular cluster), about 12,400 light-years away in the constellation of Scorpius.
The first exoplanet observed around a main sequence star with a mass of 0.468 jupiters and a semimajor axis of 0.052 AU (close enough to become tidally locked), it is the prototypical hot jupiter.
51 Pegasi b probably has a greater radius than Jupiter despite its lower mass. This is because its superheated atmosphere must be puffed up into a thick but tenuous layer surrounding it. Beneath this, the gases that make up the planet would be so hot that the planet would glow red. Clouds of silicates may exist in the atmosphere.
In 1999, this was the first extrasolar planet seen transiting its parent star, conclusively proving that the radial velocity measurements suspected to be planets actually were planets.
In 2001, astronomers using the Hubble Space Telescope announced that they had detected the atmosphere of HD 209458 b. They found the spectroscopic signature of sodium in the atmosphere, but at a smaller intensity than expected, suggesting that high clouds obscure the lower atmospheric layers.
The first planet discovered in a relatively tight triple star system.
Main Sequence Star (Orange/Yellow Dwarf)
85% Solar Mass
28% Solar Luminosity
86.5% Solar Diameter
Est. Comfort Zone: 0.540 AU
Age: 0.66 Billion Years
Notes: Star also has a Kuiper belt. Observed doppler shifts and dust depletion within 35 AU imply the presence of terrestrial planets.
Semimajor Axis: 3.3 AU
Mass: 0.86 Jupiters
Semimajor Axis: ~40 AU
Mass: ~0.1 Jupiters
Notes: Marcy et al. claim that " The Doppler behavior of magnetically active stars remains poorly explored, because so few stars are as active as Epsilon Eridani. Thus, Campbell's interpretation of a planet remains controversial." - 20 oct 02: The hypothetical planet epsilon Eridani c is suspected from the dust ring morphology.
Red dwarf star
32% Solar Mass
1.24% Solar Luminosity (largely infrared)
36% Solar Diameter
Age: 6.5 - 9.9 Billion Years
Aqueous Zone: 0.116-0.227 AU
Semimajor Axis: 0.0208 AU
Mass: 0.0185 Jupiters (7.5 Earths)
Notes: Terrestrial? One model predicts a watery ocean with an oxygen/water vapour atmosphere.
Semimajor Axis: 0.1303 AU
Mass: 0.619 Jupiters
Notes: Gas Giant? Predicted to have a cloudless upper atmosphere.
Semimajor Axis: 0.208 AU
Mass: 1.93 Jupiters
Notes: Gas Giant? Predicted to be largely cloudless, perhaps with water clouds in cooler regions.
Binary Star System
Yellow/White Dwarf
128% Solar Mass
340% Solar Luminosity
173% Solar Diameter
Est. Comfort Zone: 1.91 AU
Age: 3.3 Billion Years
Semimajor Axis: 0.0595 AU
Mass: 0.687 Jupiters
Notes: Gas Giant? Predicted to have clouds of iron and silicate in it's upper atmosphere.
Semimajor Axis: 0.830 AU
Mass: 1.97 Jupiters
Notes:Gas Giant? Predicted to be cloudless.
Semimajor Axis: 2.54 AU
Mass: 3.93 Jupiters
Notes: Gas Giant? Predicted to have water clouds
Red Dwarf Star
Semimajor Axis: 750 AU
20% Solar Mass
Binary Star System
Yellow Dwarf Star
0.95 Solar Mass
0.61 Solar Luminosity
91% Solar Diameter
Est. Comfort Zone: 0.76 AU
Age: 5.5 Billion Years
Notes: The star is surrounded by a dust disk extending at least a 40 AU, with an inclination of ~ 25o. If the planets are in the same plane than the disc, this gives to the forst planet a mas of 1.9+1.1 -0.4 MJ (Trilling & Brown 1998, Trilling et al 2000). But disc not confirmed by Schneider et al (2000b). There may by a hole with a radius of ~ 10 AU in the disk (Jayawardhana et al 2000)
Semimajor Axis: 0.038 AU
Mass: 0.045 Jupiters
Notes: Large terrestrial planet? (Chthonian planet?)
Semimajor Axis: 0.115 AU
Mass: 0.0784 Jupiters
Notes: Predicted to have a cloudless upper atmosphere with strong alkali metal absorbtion lines. Unlikely to have large moons due to tidal forces.
Semimajor Axis: 0.24 AU
Mass: 0.217 Jupiters
Notes: Gas giant?
Semimajor Axis: 5.257 AU
Mass: 3.92 Jupiters
Notes: Probably a gas giant with water clouds -- temperature is likely to be too high for ammonia clouds.
Red Dwarf Star
0.13 Solar Mass
0.0076 Solar Luminosity
30% Solar Diameter
Semimajor Axis: ~1150 AU
Orange Dwarf
86% Solar Mass
60% Solar Luminosity
96% Solar Diameter
Est. Comfort Zone: 0.753 AU
Age: 7 Billion Years
Notes: System has an extensive asteroid belt (20x more massive than ours). Star emits extensive amounts of IR.
Semimajor Axis: 0.075 AU
Mass: 0.033 Jupiters
Notes:
Semimajor Axis: 0.186 AU
Mass: 0.038
Notes:
Semimajor Axis: 0.63
Mass: 0.058
Notes: Planet is in the inner Habitable Zone?
Yellow/Orange Dwarf
108% Solar Mass
177% Solar Luminosity
143% Solar Diameter
Est. Comfort Zone: 1.34 AU
Age: 6 Billion Years
Notes:
Semimajor Axis: 0.09 AU
Mass: 0.044 Jupiters (~14 Earths)
Notes: Probably a terrestrial planet.
Semimajor Axis: 1.5 AU
Mass: 1.67 AU
Notes:
Semimajor Axis: 4.17 AU
Mass: 3.1 Jupiters
Notes:
Yellow Dwarf Star
82% Solar Luminosity
Est Comfort Zone: 0.91 AU
Semimajor Axis: 0.53 AU
Mass: 0.61 Jupiters
Notes: Probable Gas Giant
Semimajor Axis: 1.64 AU
Mass: 0.6 Jupiters
Notes: Probable Gas Giant
Semimajor Axis: 3.19 AU
Mass: 0.66 Jupiters
Notes: Probable Gas Giant
Orange Giant Star
105% Solar Mass
?% Solar Luminosity
1101% Solar Diameter
Est. Comfort Zone: 3.96-12.36 AU
Age: 0.66 Billion Years
Semimajor Axis: 1.34 AU
Mass: >8.82 Jupiters
Notes:
Brown Dwarf Star
~21 Jupiter Masses
Minor Luminosity
Mass: 3.3 Jupiter Masses
Semimajor axis: ~41 AU
Pulsar
~ 140% Solar Mass
Unknown Luminosity
~ 0.0002% Solar Radius
Notes: Discovered in 1990 and publicised in 1992, these were the first exoplanets ever verified. They are still considered highly unusual in that they orbit a pulsar.
Semimajor Axis: 0.19 AU
Mass: 0.02 Earths
Notes:
Semimajor Axis: 0.36 AU
Mass: 4.3 Earths
Notes:
Semimajor Axis: 0.46 AU
Mass: 3.9 Earths
Notes:
Semimajor Axis: 2.6 AU
Mass: 0.0004 Earths (0.2 Plutos)
Notes: Arguably the first extrasolar comet observed.
Ref: Extrasolar Planet Encyclopedia